The present invention is directed to a control system and method for internal combustion engines, and more particularly, concerns a throttle position control scheme for electronic throttle control-equipped vehicles.
Electronic airflow control systems such as electronic throttle control systems, replace traditional mechanical throttle cable systems with an xe2x80x9celectronic linkagexe2x80x9d provided by sensors and actuators in communication with an electronic controller. This increases the control authority of the electronic controller and allows the airflow and/or fuel flow to be controlled independently of the accelerator pedal position. Electronic throttle control systems include mechanisms for positioning the throttle plate in response to the driver demand and other vehicle system constraints such as a traction control system.
The most common positioning mechanism is a positioning motor. A closed-loop feedback position controller typically responds to a discrete throttle position value and commanded throttle position. Because the feedback signal is an analog signal that has been discretized by an analog-to-digital converter, its resolution is quantized and may not precisely correlate to a commanded steady-state throttle position. Thus, there is a need for an improved throttle position control system and method.
Accordingly, it is an object of the present invention to provide an improved throttle position control scheme. According to the present invention, the foregoing and other objects are obtained by a method for controlling a throttle of an electronic throttle control-equipped engine. The method comprises the steps of providing a desired throttle position derived from the driver demand and vehicle system requests. The method generates first and second throttle positions by straddling the desired throttle position within the resolution of the throttle position controller. A duty cycle is also generated as a function of the desired throttle position and system resolution. The resulting conditioned throttle position command comprising said first throttle position for a first time period and said second throttle position for a second time period is communicated to the throttle controller. The ratio of the time periods corresponds to the duty cycle such that the average throttle position command is approximately equal to the desired throttle position. In this way, the control method can achieve a desired throttle position which is, on average, of higher resolution than the throttle position sensing system.
An advantage of the present invention is that it provides higher resolution of the throttle position control. Another advantage is that the present method more accurately corresponds to the commanded steady-state throttle position as determined from the driver demand. Other objects and advantages of the invention will become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings.